The cumulative effect of air pollutants on the acute exacerbation of COPD in Shanghai, China

Background: Epidemiologic studies have shown the effect of air pollutants on acute exacerbation of chronic obstructive pulmonary disease (AECOPD). However, little is known regarding the dose-response relationship. This study aimed to investigate the cumulative effect of air pollutants on AECOPD.

Methods: We collected 101 patients with AECOPD from November 2010 through August 2011 in Shanghai. Multiple logistic regression was used to estimate associations between air pollutants and AECOPD. Poisson regression was then applied to determine the cumulative effect of air pollutants including particulate matter 10 (PM10), PM2.5, nitrogen dioxide (NO₂), sulphur dioxide (SO₂) and ozone (O₃) on AECOPD, of which the seasonal variation was further explored.

Results: The monthly episodes of AECOPD were associated with the concentrations of PM2.5 (r=0.884, p<0.05) and NO₂ (r=0.763, p<0.05). The cutoff value of PM2.5 and NO₂ for predicting AECOPD was 83.0μg/m³ and 53.5μg/m³, respectively. It showed that per 10μg/m³ increment in PM2.5 increased the relative risks (RR) for AECOPD was 1.09 with 3days cumulative effect in cold season, whereas 7days in warm season. The RR for AECOPD for per 10μg/m³ increment in NO₂ was 1.07, with a 5-day cumulative effect without seasonal variation.

Conclusions: High consecutive levels of PM2.5 and NO₂ increase the risk of developing AECOPD. Cumulative effect of PM2.5 and NO₂ appears before the exacerbation onset. These gradations were more evident in the PM2.5 during different seasons.